This project was initiated to study the role of brain neuropeptides in genetic hypertension and stress and has now been extended to study the interrelationship between different neuropeptides and their role in neuroendocrine regulation. Angiotensin-converting enzyme (ACE) activity is heterogeneously distributed in the rat brain, with highest activity in the subfornical organ. Spontaneously hypertensive rats show specific changes in ACE in intermediate and anterior pituitary lobes, and in specific nuclei of the brain stem. Changes in somatostatin occur in the pituitary and selective hypothalamic nuclei of rats lacking vasopressin.